The process for the preparation of a particulate olefin polymer catalyst component as described in the applicant's patent applications FI 981717 and FI 981718 which were not public when present application was filed, includes a step in which a fraction of a magnesium dihalide-titanium tetrahalide-carboxylic acid ester complex is recovered by precipitation from solution. This precipitation is traditionally made by contacting the solution with a large amount of an aliphatic hydrocarbon. However, such precipitation leads to a tar-like reaction product of low catalytic activity, that need to be washed several times in order to decrease the amount of unactive titanium complex. Such washing leads to a further decreased activity of the catalyst.
Aromatic hydrocarbons have also been used for the precipitation, but they lead to a very finely divided precipitate which is difficult to deposit.